1. Field of the Invention
This invention lies in the field of electrical signal transmission. More particularly, it concerns the use of pulse width modulation signals, and the accurate detection of such signals after passing through noisy transmission lines, in which the signal becomes attenuated and distorted.
Still more particularly, this invention is concerned with the design of a dynamic reference or slicing means, which is designed to separate the detected signal from noise, and to maintain an optimum ratio between the reference or slicing signal and the peak amplitude of the signal.
2. Description of the Prior Art
It is well known that a pulse width modulated signal comprises square pulses of selected widths to denote digital ones and zeros. However, when a train of ones and zeros is passed through a transmission means, the square signals distort into rounded signals. Also the peak magnitude of the signals decrease. If the signal is embedded in noise, as is usually the case, a detector or comparator must be set with a reference voltage which excludes as much as possible the noise. In conventional systems the reference voltage is set at approximately one-half the peak value of the signal, which is greater than the peak value of the noise. Whenever the signal exceeds the value of the reference signal, then the comparator indicates signal, and responds to the signal, and transmits it out through its output.
Unfortunately, if a fixed reference voltage is used in the detecting system, it is optimum only for a single length of transmission line or cable. If the reference is set for optimum use with long cable, the system becomes more susceptible to small noise perturbations. If the reference is set at the optimum for short lengths, the system will fail to work if the length of cable is increased, and the signal is sufficiently attenuated.